The public has become increasingly aware of the risk of skin cancer from overexposure to sunlight. It is widely accepted that the risk lies in overexposure to radiation within the ultraviolet (UV) region, generally considered between 8*1014 Hz to about 3.4*1016 Hz. The earth's ozone layer absorbs the vast majority of UV light from the sun, so it never reaches the surface. Humans cannot see UV light very well; the cornea generally absorbs UV radiation at the shorter wavelengths, and the eye lens strongly absorbs beyond 300 nm. For this reason, the amount of sunlight-induced radiation that we perceive ourselves as being exposed to represents only a portion of the overall radiation, the visible spectrum (generally 3.84*1014 Hz to about 7.69*1016 Hz or 455-780 nm). This visible spectrum is not a good indicator of UV light exposure, and consequent risk of skin cancer, due to variations in the earth's ozone layer that vary widely in time across the earth.
U.S. Patent Publication No. 2004/0155199 A1 describes a mobile UV-intensity indicator that is mounted on a vehicle or a portable article. The UV-intensity indicator includes a UV detector and an indicator such as a display or an alarm, and warns of overexposure under UV radiation by marking in the display or sounding the alarm. That publication does not provide a particular example of the UV-intensity indicator, but does show recognition of the need for a portable monitor of UV radiation.
It has been reported that a Japanese company, Macnica, has developed a very small UV detector for use in a cellular telephone handset that may be used as part of a UV monitoring service. The Macnica sensor is sensitive to UV light between 270-410 nm, and is reported to have almost no sensitivity to visible light.
While the need for accurate monitoring or measurement of UV light is established, the above solutions are not seen as optimum for the task. Typically, currently available UV sensors are made from silicon carbide, and are relatively expensive components. What is needed in the art is a method of monitoring or measuring UV light that may be performed by less expensive hardware components.